1. Field of the Invention
The present invention relates to a cooled grate block which forms a part of a grate for a plant for the thermal treatment of waste material.
2. Discussion of the Background
In related waste incineration plants, it is known that the waste material is conveyed on a grate through a combustion chamber and, during this process, it is dried and burnt. In addition to the transporting function, the grate also ensures constant thorough mixing of the waste material so that new surfaces of the waste material are subjected again and again to thermal treatment in the combustion chamber. For this purpose, a grate path has a plurality of grate-block rows arranged one after the other in the manner of steps, in each case fixed and movable grate-block rows following on from one another alternately. The waste material, for example refuse, located on the grate is pushed forward by a translatory movement of the movable grate-block rows and, at the same time, is thoroughly mixed. A grate-block row is formed in each case by a plurality of, generally 16 to 24, grate blocks which are suspended adjacently on a holding pipe and are braced with one another by means of a tension rod. The individual grate blocks are cooled by means of air flowing through which, at the same time, serves in combustion grates as an oxidation medium which is necessary for combustion.
Despite the air-cooling, the grate blocks are subjected to high thermal loading which results in great thermal stresses in the material of the grate blocks. Cracks may occur in the material, thus causing the risk of corrosion to rise. The grate blocks must be made of high-quality material, for example of high-alloy steel. Owing to the large thermal expansions, the size of the individual grate blocks is limited; a relatively large number of grate blocks is required in one grate-block row. It is disadvantageous in this case that certain portions of the waste material to be incinerated (bright metals, dust, etc.) drop through the gaps between the individual grate blocks, which gaps are formed by repeated expansion and contraction due to different block temperatures caused by the combustion sequence and the start up and shut down of the furnace, which portions of waste material then pass into the slag without having been burnt. If two or three grate paths are used next to one another, holders for the tension rods and seals for the leaking air must be arranged not only on the outer side of such a grate, but also between the grate paths. The exchange of individual grate blocks is thus complicated and requires long service times.